1791-16A0 Allen-Bradley Block I/O Input Module 16 Points

Allen‑Bradley 1791‑16A0 Block I/O Discrete Input Module

Product Introduction

The 1791‑16A0 from Allen‑Bradley belongs to the 1791 Block I/O series of distributed I/O products. This self‑contained module combines an I/O rack, adapter, power supply, and input devices into one unit. Specifically, it provides 16 discrete input channels operating at 120VAC. You can install these blocks in a daisy‑chain configuration to a network scanner. Therefore, the 1791‑16A0 eliminates the need for separate chassis or power supplies in small distributed applications.

Technical Specifications

Input Characteristics

• Number of inputs: Sixteen (16)

• Group configuration: 2 groups of 8

• Nominal input voltage: 120VAC

• On‑state voltage range: 79‑132VAC, 47‑63 Hz

• On‑state current: 5mA @ 79V minimum

• Off‑state voltage maximum: 35VAC

• Off‑state current minimum: 2.3mA

External Power Requirements

• Voltage range: 85‑132VAC, 47‑63 Hz

• Current draw: 150 mA

Output Ratings (Internal/Pass‑through)

• Maximum output rating: 600mA @ 30°C

• Maximum output rating: 300mA @ 60°C

• Maximum surge current: 10A for 50ms (repeatable every 2 seconds)

Physical & Environmental

• Mounting options: Vertical or Horizontal

• Maximum operating temperature: 60°C (140°F)

• Weight: 1.25 lbs (0.57 kg)

• UPC: 612598127047

Compatible Field Instruments

The 1791‑16A0 supports integration with various discrete field devices. Specifically, you can connect:

• Proximity switches

• Limit switches

• Selector switches

• Float switches

• Pushbutton switches

• Auxiliary contacts

Additionally, this module works with other discrete operating devices that meet the voltage and current specifications. Therefore, you gain flexibility when designing control panels.

System Architecture & Integration

The 1791 Block I/O family, including the 1791‑16A0, features built‑in functionalities. Each block contains an I/O rack, adapter, power supply, and I/O devices. Install these blocks in a daisy‑chain configuration to a scanner. The scanner typically resides in a PLC controller chassis. Inputs and outputs transfer asynchronously between the block I/O and the controller.

Compatibility with 1771 Output Modules
The 1791‑16A0 works with select 1771 series output modules. However, you must verify two conditions. First, the output module's off‑state leakage current must stay below the Block I/O's minimum OFF‑state current. Second, the Block I/O's minimum ON‑state voltage must exceed the supply voltage minus the ON‑state voltage drop across the 1771 module.

Compatible 1771 output modules include:

• 1771‑OAN

• 1771‑OD16

• 1771‑ODD

• 1771‑ODZ

• Other modules meeting the compatibility requirements

Mounting & Installation Guidelines

Physical Installation Steps

1. Choose either vertical or horizontal mounting orientation for the 1791‑16A0.

2. Maintain 2 inches (58.0 cm) clearance on all sides of the module. This allows adequate airflow for ventilation.

3. Secure the module firmly to the mounting surface using appropriate hardware.

4. Connect the external power supply within 85‑132VAC, 47‑63 Hz.

5. Wire input devices to the 16 channels according to your group configuration.

6. Connect the daisy‑chain communication link to the network scanner.

Temperature Considerations
First, the maximum output rating changes with temperature. At 30°C, the 1791‑16A0 supports 600mA. At 60°C, this rating drops to 300mA. Next, the surge current rating remains 10A for 50ms regardless of temperature. However, you must allow at least 2 seconds between surge events. Therefore, plan your load distribution carefully for high‑temperature environments.

Why Choose This 1791‑16A0 Block I/O?

Space Savings – Combines power supply, adapter, and I/O into one compact block.
Simplified Wiring – No separate chassis or backplane required for installation.
Flexible Mounting – Supports both vertical and horizontal orientations.
Proven Reliability – Allen‑Bradley's 1791 series is widely used in factory automation.

In comparison to rack‑based I/O systems, the 1791‑16A0 reduces component count significantly. Moreover, its self‑contained design lowers total installation costs. Consequently, this module suits small to medium distributed control applications.

Packaging List

• 1 x Allen‑Bradley 1791‑16A0 Block I/O module (16 input channels)

• No mounting hardware included (user supplies based on surface)

• No communication cables included

• No additional certificates or warranty documents included

Note: The product ships in anti‑static packaging without extended warranty or calibration certificates.

Shipping Information

• Carrier options: FedEx, UPS, DHL

• Packaging dimensions: 8.0 x 6.0 x 3.5 inches (estimated)

• Gross weight: 1.25 lbs (0.57 kg)

• Standard lead time: 2–5 business days after order processing

Frequently Asked Questions (FAQ)

1. Is the 1791‑16A0 compatible with modern ControlLogix or CompactLogix PLCs?
Yes, the 1791‑16A0 works with these PLCs through a compatible scanner module. You need a 1771 or 1794 series scanner that supports block I/O communication. The module communicates asynchronously with the controller via the daisy‑chain network.

2. What happens if I exceed the 600mA output rating at 30°C?
Exceeding 600mA may cause internal overheating and permanent damage. Additionally, the module could trip internal protection circuits. Therefore, always calculate your total load current before operation. For loads above the rating, use an external interposing relay.

3. Can I mix input and output devices on the same 1791‑16A0?
No, the 1791‑16A0 provides 16 inputs only. This module has zero output channels. For mixed I/O requirements, consider other 1791 series blocks with both input and output channels. Alternatively, use separate input and output blocks in the same daisy chain.

4. How do I verify if my existing 1771 output module works with this block?
Check the 1771 module's datasheet for two values. First, the off‑state leakage current must be less than 2.3mA. Second, the ON‑state voltage drop must allow the 1791‑16A0 to see at least 79VAC. Modules like 1771‑OAN, 1771‑OD16, 1771‑ODD, and 1771‑ODZ typically meet these requirements.

5. What is the difference between 1791‑16A0 and 1769‑16A0?
The 1791‑16A0 is a Block I/O module for distributed applications. The 1769 series serves CompactLogix local I/O and is not interchangeable. Always verify your system's compatibility guide before ordering.